When coupling an implement to a machine where the implement is to be powered by an output shaft of the machine, it is desirable during startup to have the output shaft of the machine free to rotate about 60 degrees for coupling to the implement but not allow the output shaft to rotate more than 180 degrees from origin. It can be difficult to have the output shaft of the machine operate within these parameters under certain conditions. These parameters may vary for different machines and/or implements.
An exemplary condition where it is difficult for the machine engine powering the output shaft to operate within the above parameters is during cold start (for example, −30° C. or below). In some systems, a brake powered by a fluid pump is used to prevent the output shaft from rotating more than 180 degrees during start up. The fluid pump pulls fluid up a channel from a reservoir to engage the brake. During cold start conditions, the fluid can be very viscous and can take several seconds for the fluid pump to build brake pressure to pull the high viscous fluid up the channel and energize the brake system. So it may take several seconds for the brake volume to fill and apply any braking to the output shaft that has been running since start up.
One attempted solution to this problem is to have three pins equally spaced about the axis of the clutch center line. However, the output shaft can break these pins if the fluid pressure drops suddenly. Another disadvantage of this solution is that the piston and brake cone interface can be steel-on-steel which wears poorly and produces unwanted heat. An alternative design is to use steel piston and brake cone with roller balls instead of pins. In this alternative, the balls can wedge and create flat spots and produce a cyclic failure with the ball and ramp design. The common drawbacks with these attempted solutions to the “free” rotation and braking issues are: (1) whether it's a ball or pin, they will both fail with sudden loss of pressure; (2) steel-on-steel designs wear quickly; (3) the amount of braking pressure applied to the output shaft is only that of the Bellville springs utilized to push the piston back, and a high inertia implement can take minutes to spin down and risk snapping the pins if the steel-on-steel interface fails; and (4) the “free rotation” for coupling the implement is not actually free; in that there is constant pressure on the thrust bearing from the clutch Bellville springs.
It would be desirable to have a system that allows limited rotation of an engine output shaft to enable coupling of an implement to the output shaft while simultaneously preventing complete rotation of the output shaft. It would also be desirable to have such a system function in any conditions, including extreme cold, and to have such a system shutdown gracefully during a failure mode, such as a loss of hydraulic pressure.